The Ras oncogene mediates a variety of biological effects which promote tumorigenic transformation. However, activated forms of Ras also have a surprising number anti-transformation aspects. They can induce senesence, cell cycle arrest and even death by apoptosis. The mechanisms behind these anti-neolastic effects remain poorly understood. We have identified a famiuly of novel Ras effectors which appear to mediate some of the anti-neoplastic activities of Ras. especialy apoptosis. At least one of these genes is frequently deranged during the development of human cancers and so this group of Ras effectors may be a family of Ras regulated tumor suppressors.